* {
  padding: 0;
  margin: 0;
}
li {
  list-style: none;
}
.header {
  width: 600px;
  height: 300px;
  margin: 0 auto;
  background-color: skyblue;
}
.header .nav {
  display: flex;
}
.header .nav .active {
  background-color: steelblue;
}
.header .nav h3 {
  width: 200px;
  line-height: 60px;
  text-align: center;
}
.header ul.active {
  display: block;
}
.header ul {
  margin-top: 20px;
  display: none;
}
.header ul li {
  height: 30px;
  line-height: 30px;
}
.header ul button {
  margin-top: 4px;
  width: 80px;
  height: 30px;
  line-height: 30px;
  text-align: center;
}
